February 2009

What is MRI for the Breast?

Magnetic resonance imaging (MRI) is a diagnostic procedure that uses a combination of a large magnet, radiofrequencies, and a computer to produce detailed images of organs and structures within the body.

MRI does not use radiation, as do x-rays or computed tomography (CT scans).

A magnetic field is created and pulses of radio waves are sent from a scanner. The radio waves knock the nuclei of the atoms in your body out of their normal position. As the nuclei realign into proper position, they send out radio signals.

These signals are received by a computer that analyzes and converts them into an image of the part of the body being examined. This image appears on a viewing monitor. Some MRI machines look like narrow tunnels, while others are more open.

For a breast MRI, the woman usually lies face down, with her breasts positioned through openings in the table. In order to check breast positioning, the technologist watches the MRI through a window while monitoring for any potential movement.

A breast MRI usually requires the use of a contrast dye that is injected into a vein in the arm before or during the procedure. The dye may help create clearer images that outline abnormalities more easily.

MRI, used with mammography and breast ultrasound, can be a useful diagnostic tool.

Recent research has found that MRI can locate some small breast lesions sometimes missed by mammography.

It can also help detect breast cancer in women with breast implants and in younger women who tend to have dense breast tissue.

Mammography may not be as effective in these cases. Since MRIs do not use radiation, they may be used to screen women younger than 40 and to increase the number of screenings per year for women at high risk for breast cancer.

Although it has distinct advantages over mammography, breast MRI also has potential limitations. For example, it is not always able to distinguish the difference between cancerous abnormalities, which may lead to unnecessary breast biopsies. This is often referred to as a "false positive" test result.

Recent research has demonstrated that using commercially available software programs to enhance breast MRI scans can reduce the number of false positive results with malignant tumors. Thus, the need for biopsies may decrease with computer-aided enhancement.

Another disadvantage of breast MRI is that it has historically been unable to identify calcifications or tiny calcium deposits that can indicate breast cancer.